Korg DW-6000 detuned voices

[beep]

Hello,

I have a Korg DW-6000 here and the pitch on two to four of the six voices (depending on which note I play) is slightly lower when I cycle through the voices.

The keys, where the problem occurs change with pitchbend / master tuning changes but not when I change the master clock frequency (trimpot on the
DWGS board)

It's weird, cause those are digital oscillators but they act like a timbre wolf

The trim pots allow only level adjustment for the vca and cutoff/reso. how can I adjust the oscillators?

thanks in advance.